The invention relates to a fuel injection system for a mixture-compressing, externally ignited internal combustion engine employing continuous injection into a suction tube.
Disposed within the suction tube are, sequentially, a measuring member and an arbitrarily actuatable butterfly throttle valve. The measuring member moves in response to the amount of air flowing through the suction tube and against a resetting force, thus setting the movable member of a valve disposed in the fuel line of the engine for the purpose of metering out a quantity of fuel proportional to the air quantity. The metering process takes place while a constant pressure difference exists across the valve. The magnitude of this pressure difference can, however, be changed, in dependence on engine parameters, by a hysteresis-free electromagnetic assembly. The assembly includes a permanent magnet and a moving coil armature, and acts upon a first differential pressure valve, embodied as a flat seat diaphragm valve. The diaphragm can be moved, by the force of a spring and also by the variable force due to the electromagnetic assembly, in the direction tending to open the first differential pressure valve.
In a known fuel injection system of this kind, the pressure difference prevailing at a metering and quantity divider valve is changeable by means of a second differential pressure valve. The internal operation of the differential pressure valves associated with the metering and quantity divider valve is based entirely on the diaphragm rigidity, i.e., without a spring counter force. This embodiment requires that the diaphragm be installed in the metering and quantity divider valve without stresses or deformations. In order to save constructional space and to make the fuel lines as short as possible, it is desired to locate the additional differential pressure valve within the metering and quantity divider valve. This brings the risk however, that during the assembly, the spring of the additional differential pressure valve will cause stresses and deformations in the diaphragm.